1. Field of the Invention
The present invention relates to the field of acoustic test chambers or cells. More particularly, the invention is directed to an apparatus and method for providing an acoustic test chamber or cell that achieves, in air, very high-intensity infrasonic to low-sonic frequencies in moderately large test volumes with very pure sinusoidal waveforms.
2. Description of Related Art
High-intensity acoustic test chambers are well known in the art. Previous high-intensity acoustic test chambers capable of operation at fundamental frequencies below 100 Hz include high-intensity flow-modulator-driven non-resonant chambers, standing-wave resonant chambers driven by flow modulators or loudspeakers, and piston-driven sealed chambers.
Each of these known high-intensity acoustic test chambers has significant limitations. High-intensity flow-modulator-driven non-resonant chambers as devices are not capable of efficient operation or the production of reasonably undistorted sound (sine waves) below about 30 Hz.
Standing-wave resonant chambers driven by flow modulators or loudspeakers, by their nature, have strongly non-uniform acoustic fields in their test volumes and require that the test chamber have a long dimension of at least one-half the wavelength of the lowest usable frequency. That is, their long dimension must be at least 11 m's at 30 Hz.
Piston-driven sealed chambers require a mechanical drive to accelerate and decelerate a piston which serves as one wall of a test chamber or test cell. This acceleration/deceleration takes place at very high rates which restricts these devices to very low frequencies and small test volumes, typically less than 1 m3.